"It's like fighting in the dark," Walter commented. "If we only knew just what we are up against, we would know better what to expect. This mystery business is something I don't fancy." "It's up to us to solve it," said his chum; "and I'm going to have a try at the job to-morrow. It's comforting, anyway, to hear that machine working so steadily. That Bratton is sure doing some digging. Hear how regular that bucket is dumped. I wonder what those two long and two short whistles mean." "That's the signal to move track and back up," said Walter, proud of his newly acquired knowledge. "One short whistle means go ahead, three long ones are for the teamster; four long ones are the distress signal, and five long ones is the signal for everyone to come to the machine." "The men must all be told what that last signal means," said Charley thoughtfully. "It may come handy some time." As night drew near, the resting crews emerged, yawning, from their tents, and began to prepare for their night's work. Lanterns were filled and cleaned and working clothes donned. Chris, with his assistant's help, filled up a large basket with food, which, at sundown, was sent out to the workers on the machine. Supper was eaten, and all the Americans gathered around the campfire and told stories and jokes in its genial glow. The Spaniards built another fire, in front of their own tents, and sang Spanish songs to the accompaniment of a couple of mandolins, while Chris and Sam, his new assistant, lounging in the cook tent, talked lovingly about their own country, the poverty-stricken Bahama Islands. "This is a mighty different camp from what it was four days ago," remarked McCarty. "There was no music or laughing going on then. All you could hear was grumbling and cursing. Believe me, I like this new order better." When 8 o'clock came, Kitchner called his crew and left for the machine, from which soon came Bratton with his tired crew. "Digging's good," he said, in answer to McCarty's questions. "She's hitting a little rock, but it's soft and digs easy. I struck one dead head, but got it out without much trouble." "What's a dead head?" Walter asked. "Submerged stumps or trees," McCarty explained. "We often come upon them in our digging. They are generally big, hard as iron, and mean to get out. One does not see them until the bucket hits them, and then the machine is too close to use dynamite." "Queer," the other commented. "Yes," McCarty agreed. "There are forests buried below us, I suppose. The process of building up and tearing down goes on all the time. In the centuries to come, likely, these trees around us will be buried in turn, and another forest rise above them." "The Lord moves in a mysterious way His wonders to perform," quoted the Captain reverently.